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1) No, I wouldn't. Alot of bitcoin users use adresses from exchanges such as bittrex/poloniex, where you do not have control of the adress from which the coins are spent from.

2) I'm not really sure what you mean by this, I don't see why you would use the same adress multiple times in the first place, but as you previously stated this is not an issue for you, so why would it be after a refund?

3) Not sure about different wallets, but in electrum for example you will be able to sent the changeback to an adress you choose, or, completely disable it. So yes, this should be possible.

On bitcoin core -> to remove change adresses or set custom ones, Follow:

It is highly recommended that you do not do this as address reuse is not recommended.
If you are sure that you want to reuse change addresses, go to Settings > Options and then the Wallet tab. Check the box for "Enable coin control features". Then click OK. When you go to send, you will now see a box for Coin Control. Check the box for "Custom Change address" and then enter the address that you want to use as your change address. Then send your Bitcoin and the change will go to wherever you specified.